Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RETORTABLE PACKAGING FILM WITH OUTER LAYERS CONTAINING BLEND
OF PROPYLENE-BASED POLYMER AND HOMOGENEOUS POLYMER
Field of the Invention
The present invention relates generally to packaging films, and more
specifically
to packaging films suitable for packaging food products which are to undergo
retort while
remaining inside the package.
Background of the Invention
Pouches made from films or laminates, including polymers such as polyethylene
or polypropylene, have found use in a variety of applications. For example,
such pouches
are used to hold low viscosity fluids (e.g., juice and soda), high viscosity
fluids (e.g.,
condiments and sauces), fluid/solid mixtures (e.g., soups), gels, powders, and
pulverulent
materials. The benefit of such pouches lies, at least in part, in the fact
that such pouches
are easy to store prior to filling and produce very little waste when
discarded. The
pouches can be formed into a variety of sizes and shapes.
Pouches can be assembled from films, laminates, or web materials using
vertical
form-fill-seal (VFFS) machines. Such machines receive the film, laminate, or
web
material and manipulate the material to form the desired shape. For example,
one or more
films, laminates, and/or web materials can be folded and arranged to produce
the desired
shape. Once formed, the edges of the pouch are sealed and the pouch filled.
Typically, the
film, laminate, or web material has at least one heat seal layer or adhesive
surface which
enables the edges to be sealed by the application of heat.
During the sealing process, a portion of at least one edge of the pouch is
left
unsealed until after the pouch is filled. The pouch is filled through the
unsealed portion
and the unsealed portion is then sealed. Alternatively, the pouch can be
filled and the
unsealed portion simultaneously closed in order to provide a sealed pouch with
minimal
headspace. The VFFS process is known to those of skill in the art, and
described for
example in U.S. Pat. No. 4, 589,247 (Tsurata et al), incorporated herein by
reference. A
flowable product is introduced through a central, vertical fill tube to a
formed tubular film
having been sealed transversely at its lower end, and longitudinally. The
pouch is then
completed by sealing the upper end of the tubular segment, and severing the
pouch from
the tubular film above it.
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Retortable form fill and seal packaging can be carried out by providing a
backseam seal and a bottom seal, followed by filling the resulting packaging
article and
thereafter sealing it closed and cutting it free of the film upstream. The
packaged product
is thereafter placed on a retort rack. The film needs to form a heat seal
capable of
withstanding retort conditions and provide high flex crack and vibration
induced abuse
resistance. The film also needs to be able to readily release (i.e., not
stick) from the retort
racks. Otherwise the pull force on the pouch may produce package damage. It is
also
beneficial that the film is so sticky that it places undesirable drag on filni
processing
equipment. It would also desireable for the flm to be capable of forming a
strong lap seal
which can withstand retort conditions. However, an outside layer which readily
seals to
the inside layer to form a lap seal generally also sticks to the retort rack
and provides
unwanted drag on fihn processing equipment. It would be desirable to have a
retortable
multilayer film which is readily lap sealable and also avoids sticking to the
retort rack.
Summary of the Invention
The retortable multilayer film of the present invention utilizes outer layers
each
containing a blend of a homogeneous propylene-based polymer and a homogeneous
ethylene/alpha-olefin copolymer. Such a blend in each outer layer of a
retortable
multilayer film has been found to be capable of providing strong lap
sealability while at
the same time releasing from the retort racks and having low enough slip
properties to
avoid unwanted drag on film processing equipment.
As a first aspect, the present invention is directed to a retortable
multilayer
packaging film having a crosslinked first outer layer which serves as a heat
seal layer/
product-contact layer. This first outer layer comprises a blend of (i) a
homogeneous
propylene-based polymer and (ii) a homogeneous ethylene/C4_2Q alpha-olefin
copolymer
having a density of from about 0.86 g/cc to about 0.91 g/cc. The packaging
film further
comprises a crosslinked second outer layer that serves as a heat seal/skin
layer. This
second outer layer also comprises a blend of (i) a homogeneous propylene-based
polymer
and (ii) a homogeneous ethylene/C4_20 alpha-olefin copolymer having a density
of from
about 0.86 g/cc to about 0.91 g/cc. Although both the first outer layer and
the second
outer layer each comprise a blend of a homogeneous propylene-based polymer and
a
homogeneous ethylene/C4_20 alpha-olefin copolymer, the first and second outer
layers can
be of the same chemical composition or of different chemical composition.
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Preferred homogeneous propylene-based polymers in the outer heat seal/product
contact layer include both homogeneous propylene homopolymer and homogeneous
propylene copolymer. It is preferred that the homogeneous propylene-based
polymer has
a density of from about 0.85 g/cc to about 0.90 g/cc. It is also preferred
that the
homogeneous propylene-based polymer has a melt index of from about 1 to about
50.
In a preferred embodiment, the homogeneous propylene-based polymer in the
outer heat seal/product contact layer comprises at least one member selected
from the
group consisting of a homogeneous isotactic propylene/butene copolymer having
a
melting point of from about 110 C to about 150 C, and a homogeneous
syndiotactic
propylene-based polymer.
In a preferred embodiment, the a homogeneous ethylene/C4_20 alpha-olefin
copolymer in the outer heat seal/product contact layer has a density of from
about 0.88
g/cc to about 0.905 g/ce.
Preferred homogeneous propylene-based polymers in the outer heat seal/skin
layer
also include both homogeneous propylene homopolymer and homogeneous propylene
copolymer. It is also preferred that the homogeneous propylene-based polymer
has a
density of from about 0.85 g/cc to about 0.90 g/cc. It is also preferred that
the
homogeneous propylene-based polymer has a melt index of from about 1 to about
50.
In a preferred embodiment, the homogeneous propylene-based polymer in the
outer heat seal/skin layer comprises at least one member selected from the
group
consisting of a homogeneous isotactic propylene/butene copolymer having a
melting
point of from about 110 C to about 150 C, and a homogeneous syndiotactic
propylene-
based polymer.
In one preferred embodiment, the homogeneous propylene-based polymer in the
outer heat seal/skin layer has a melting point of at least 125 C, in order to
provide the
outer heat seal/skin layer with good release from metal retort racks.
In one preferred embodiment, the homogeneous propylene-based polymer in the
outer heat seal/skin layer includes a homogeneous syndiotactic propylene-based
polymer
having a density of from about 0.86 g/cc to about 0.87 g/cc. A homogeneous
syndiotactic
propylene-based polymer with a melting point of 130 C and a density of 0.87
provides
good abuse-resistance in the outer heat seal/skin layer.
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In a preferred embodiment, the a homogeneous ethylene/C4_20 alpha-olefin
copolymer in the outer heat seal/skin layer has a density of from about 0.88
g/cc to about
0.905 g/cc.
In a preferred embodiment, the retortable multilayer packaging film further
comprises an 02-barrier layer, with the grease and fat-resistant layer being
between the
heat seal layer and the 02-barrier layer.
In a preferred embodiment, the 02-barrier layer comprises at least one member
selected from the group consisting of crystalline polyamide, amorphous
polyamide,
ethylene/vinyl alcohol copolymer, vinylidene chloride copolymer, and
polyacrylonitrile.
In a preferred embodiment, the outer heat seal/product contact layer comprises
a
blend of at least one member selected from the group consisting of (i) a
homogeneous
isotactic propylene/ethylene copolymer having a having a density of from about
0.88 g/cc
to about 0.90 g/cc and a melting point of from about 110 C to about 150 C, and
(ii) a
homogeneous ethylene/butene copolymer having a density of from about 0.90 g/cc
to
about 0.91 g/cc.
In a preferred embodiment, the outer heat seal/skin layer comprises a blend of
at
least one member selected from the group consisting of: (i) a homogeneous
isotactic
propylene/ethylene copolymer having a having a density of from about 0.88 g/cc
to about
0.90 g/cc and a melting point of from about 125 C to about 150 C, and(ii) a
homogeneous ethylene/butene copolymer having a density of from about 0.90 g/cc
to
about 0.91 g/cc.
In a preferred embodiment, the outer heat seal/product contact layer further
comprises a slip agent and an anti-blocking agent, and the crosslinked second
layer
further comprises a slip agent and an anti-blocking agent.
In a preferred embodiment: (a) the isotactic homogeneous propylene-based
polymer in the outer heat seal/product contact layer comprises isotactic
homogeneous
propylene/ethylene copolymer having a density of from about 0.88 g/cc to about
0.90
g/cc, and the homogeneous ethylene/C4_8 alpha-olefin copolymer comprises
homogeneous
ethylene/butene copolymer having a density of from about 0.88 g/cc to about
0.905 g/cc,
and (b) the isotactic homogeneous propylene-based polymer in the outer heat
seal/skin
layer comprises isotactic homogeneous propylene/ethylene copolymer having a
density of
from about 0.88 g/cc to about 0.90 g/cc, and the homogeneous ethylene/C4_8
alpha-olefin
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copolymer comprises homogeneous ethylene/butene copolymer having a density of
from
about 0.88 g/cc to about 0.905 g/cc.
In a preferred embodiment, the crosslinked outer heat seal/skin layer further
comprises a slip agent and an antiblocking agent.
5 In a preferred embodiment, the retortable multilayer film further comprises
a tie
layer between the 02-barrier layer and the crosslinked second layer.
In a preferred embodiment, the retortable multilayer film further comprises a
grease and fat-resistant layer between the 02-barrier layer and the
crosslinked first layer.
In a preferred embodiment, the grease-resistant layer also functions as a tie
layer
between the 02-barrier layer and the outer heat seal /product contact layer.
In a preferred embodiment, the retortable multilayer film further comprises a
first
high temperature abuse layer between the crosslinked outer heat seal/product
contact
layer and the 02-barrier layer, and a second high temperature abuse layer
between the
crosslinked outer heat seal/skin layer and the 02-barrier layer.
In a preferred embodiment, the retortable multilayer film further comprises a
first
low temperature abuse layer between the grease and fat-resistant layer and the
2-barrier
layer, and a second low-temperature-abuse layer between the 02-barrier layer
and the
crosslinked outer heat seal/skin layer.
In a preferred embodiment, the grease and fat-resistant layer comprises at
least
one member selected from the group consisting of: (i) a crystalline anhydride-
grafted C2_
3/C6_2o alpha-olefin copolymer having a density of from 0.93 g/cc to 0.97
g/cc, (ii) a
crystalline C2_3/butene copolymer having a density of at least 0.92 g/cc,
(iii) ionomer
resin, and (iv) ethylene/unsaturated acid copolymer.
In a preferred embodiment, the first high-temperature-abuse layer and the
second
high-temperature-abuse layer each comprise at least one member selected from
the group
consisting of seimcrystalline polyamide comprising at least one member
selected from the
group consisting of polyamide-6, polyamide-6,6, polyamide-6,9, polyamide-4,6,
and
polyamide-6,10.
In a preferred embodiment, the first low-temperature-abuse layer and the
second
low-temperature-abuse layer each comprise at least one member selected from
the group
consisting of olefin homopolymer, C2_3/C3_20 alpha-olefin copolymer, and
anhydride-
grafted ethylene/alpha-olefin copolymer.
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In a preferred embodiment, the tie layer comprises at least one member
selected
from the group consisting of anhydride grafted ethylene/alpha-olefin
copolymer, ionomer
resin, ethylene/unsaturated acid copolymer.
In a preferred embodiment, at least one of the high-temperature-abuse layers
comprises a blend of the high-temperature-abuse polymer and at least one
medium-
temperature-abuse polymer selected from the group consisting of polyamide-
6/6,6,
polyamide-6,12, polyamide-6/6,9, polyamide-12, and polyamide- 11.
In a preferred embodiment, the retortable multilayer film further comprises at
least
one medium-temperature-abuse layer comprising at least one medium-temperature-
abuse
polymer having Tg of from 16 C to 49 C. Preferably, the medium-temperature-
abuse
polymer comprises at least one member selected from the group consisting of
polyamide-
6/6,6, polyamide-6,12, polyamide-6/6,9, polyamide-12, and polyamide-11.
As a second aspect, the present invention is directed to a retortable
packaging
article comprising a multilayer packaging film heat sealed to itself. The
multilayer
packaging film is in accordance with the first aspect of the present
invention.
In a preferred embodiment, the crosslinked outer heat seal/product contact
layer is
heat sealed to the crosslinked outer heat seal/skin layer.
In a preferred embodiment, the crosslinked outer heat seal/product contact
layer is
heat sealed to itself.
In a preferred embodiment, the retortable multilayer pacckaging film is heat
sealed to itself to form a member selected from the group consisting of end-
seal bag, side-
seal bag, pouch, and casing.
In a preferred embodiment, the article exhibits less than 19% leaking packages
when filled with water, sealed closed and retorted at 250 F for 90 minutes in
a vibration
table test in accordance with ASTM 4169 Assurance Level II for 30 minutes of
vibration.
As a third aspect, the present invention is directed to a retortable packaged
product
comprising a product surrounded by a multilayer packaging film heat sealed to
itself. The
multilayer packaging film is in accordance with the first aspect of the
present invention.
As a fourth aspect, the present invention is directed to a process of
preparing a
retorted packaged product, comprising: (A) placing a product in a packaging
article
comprising a multilayer packaging film heat sealed to itself; (B) sealing the
article closed
so that the product is surrounded by the multilayer packaging film; and (C)
heating the
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packaged product to a temperature of at least 220 F for a period of at least 1
hour. The
multilayer packaging film is in accordance with the first aspect of the
present invention.
In a preferred embodiment, the product comprises at least one member selected
from the group consisting of chili, rice, beans, olives, beef, pork, fish,
poultry, corn, eggs,
tomatoes, and nuts. The product can comprise any food, including meat, chicken
broth,
tomato-based products, etc.
In a preferred embodiment, the packaged product is heated to a temperature of
at
least 230 F for a period of at least about 75 minutes.
In a preferred embodiment, the packaged product is heated to a temperature of
at
least 240 F for a period of at least about 90 minutes.
In a preferred embodiment, the packaged product is heated to a temperature of
at
least 240 F for a period of at least about 2 hours.
In a preferred embodiment, the packaged product is heated to a temperature of
at
least 250 F for a period of at least about 90 minutes.
In a preferred embodiment, the food product in the package has a weight of
from
about 0.5 to about 10 kilograms, preferably from about 3 to about 5 kilograms.
Detailed Description of the Invention
As used herein, the verb "to retort" refers to subjecting an article, such as
a
packaged food product, to sterilizing conditions of high temperature (i.e., of
from 212 F
to 300 F) for a period of from 10 minutes to 3 hours or more, in the presence
of water,
steam, or pressurized steam. As used herein, the phrase "retortable film"
refers to a
packaging film that can be formed into a pouch, filled with an oxygen-
sensitive product,
heat sealed, and retorted without delamination the layers of the film. The
retort process is
also carried out at elevated pressure. In general, the retort process is
carried out with the
packaged products being placed in an environment pressurized to from 20 to 100
psi. In
another embodiment, from 30 to 40 psi.
As used herein, the term "film" is inclusive of plastic web, regardless of
whether it
is film or sheet. Preferably, films of and used in the present invention have
a thickness of
0.25 mm or less. Preferably, the retortable film of the present invention has
a thickness
of from 2 to 15 mils, more preferably from 4 to 8 mils.
Preferably, the film of the present invention is produced as a fully
coextruded
film, i.e., all layers of the film emerging from a single die at the same
time. Preferably,
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the fihn is made using a flat cast film production process or a round cast
film production
process. Alternatively, the film can be made using a blow film process.
The multilayer retortable film of the present invention can be either heat-
shrinkable or non-heat shrinkable. If heat-shrinkable, the film can exhibit
either
monoaxial orientation or biaxial orientation. As used herein, the phrase "heat-
shrinkable"
is used with reference to films which exhibit a total free shrink (i.e., in
both machine and
transverse directions) of at least 10% at 185 F, as measured by ASTM D 2732,
which is
hereby incorporated, in its entirety, by reference thereto. If not heat
shrinkable, the film
can have been heat set during its manufacture. All films exhibiting a total
free shrink of
less than 10% at 185 F are herein designated as being non-heat-shrinkable.
As used herein, the term "package" refers to packaging materials configured
around a product being packaged. The phrase "packaged product," as used
herein, refers
to the combination of a product which is surrounded by a packaging material.
. As used herein, the phrases "inner layer" and "internal layer" refer to any
layer, of
a multilayer film, having both of its principal surfaces directly adhered to
another layer of
the film.
As used herein, the phrase "outer layer" refers to any film layer of film
having less
than two of its principal surfaces directly adhered to another layer of the
film. The phrase
is inclusive of monolayer and multilayer films. In multilayer films, there are
two outer
layers, each of which has a principal surface adhered to only one other layer
of the
multilayer film. In monolayer films, there is only one layer, which, of
course, is an outer
layer in that neither of its two principal surfaces are adhered to another
layer of the film.
Once the retortable multilayer film is heat sealed to itself and thereby
converted
into a packaging article, one outer layer of the film is an inside layer of
the article and the
other outer layer becomes the outside layer of the article. The inside layer
can be referred
to as an "outer heat seal/product contact layer". The other outer layer can be
referred to
as an "outer heat seal/skin layer".
As used herein, the phrase "inside layer" refers to the outer layer of a
multilayer
film packaging a product, which is closest to the product, relative to the
other layers of
the multilayer film.
As used herein, the phrase "outside layer" refers to the outer layer, of a
multilayer
film packaging a product, which is furthest from the product relative to the
other layers of
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the multilayer film. Likewise, the "outside surface" of a bag is the surface
away from the
product being packaged within the bag.
As used herein, the term "adhered" is inclusive of films which are directly
adhered
to one another using a heat seal or other means, as well as films which are
adhered to one
another using an adhesive which is between the two films.
As used herein, the phrases "seal layer," "sealing layer," "heat seal layer,"
and
"sealant layer," refer to an outer film layer, or layers, involved in heat
sealing of the film
to itself, another film layer of the same or another film, and/or another
article which is not
a film. Heat sealing can be performed by any one or more of a wide variety of
manners,
such as using a heat seal technique (e.g., melt-bead sealing, thermal sealing,
impulse sealing,
ultrasonic sealing, hot air, hot wire, infrared radiation, etc.). A preferred
sealing method
uses the same double seal bar apparatus used to make the pressure-induced seal
in the
examples herein. A heat seals is a relatively narrow seal (e.g., 0.02 inch to
1 inch wide)
across a film.
As used herein, the phrase "grease-resistant layer" refers to a film layer
which is
resistant to grease, fat, and/or oil, i.e., a layer which does not swell and
delaminate from
adjacent layers upon exposure to grease, fat, and/or oil during retorting of a
package made
using the film. The ability of a film to resist grease during retort is
measured by
packaging a high grease content food product in the film (e.g., corn oil,
chili, etc)
followed by retorting the packaged product. The retorted package is then
inspected
immediately at the conclusion of retort cycle, to determine if there has been
any layer
delamination. If no delamination, the product is stored and checked again one
week later,
and every two weeks thereafter for a total of at least 5 weeks from the date
of retort. If no
visible sign of delamination is present, the film is determined to be a grease-
resistant film.
As used herein, the phrase "high temperature abuse layer" refers to a film
layer
containing a polymer capable of contributing substantial abuse resistance when
the
package is subjected to abuse while in the temperature range of from about 60
C to about
180 C. Polymers capable of providing high temperature abuse resistance are
polymers
having a Tg of from 50 C to 125 C. Preferred polymers for providing high
temperature
abuse resistance include semicrystalline polyamides, particularly polyamide-6,
polyamide-6,6, polyamide-6,9, polyamide-4,6, and polyamide-6,10.
As used herein, the phrase "medium temperature abuse layer" refers to a film
layer containing a polymer capable of contributing substantial abuse
resistance when the
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package is subjected to abuse while in the temperature range of from about 20
C to about
60 C. Polymers capable of providing medium temperature abuse resistance are
polymers
having a Tg of from 16 C to 49 C. Preferred polymers for providing medium
temperature abuse resistance include polyamide-6/6,6, polyamide-6,12,
polyamide-6/6,9,
5 polyamide-12, and polyamide-11.
As used herein, the phrase "low temperature abuse layer" refers to a film
layer
containing a polymer capable of contributing substantial abuse resistance when
the
package is subjected to abuse while in the temperature range of from about -50
C to
about 20 C. Polymers capable of providing low temperature abuse resistance are
10 polymers having a Tg of up to 15 C. Preferred polymers for providing low
temperature
abuse resistance include olefin homopolymers, C2_3/C3_20 alpha-olefin
copolymer, and
anhydride-grafted ethylene/alpha-olefin copolymer.
One measure of abuse resistance for a package containing a flowable product is
ASTM D 4169 "Standard Practice for Performance Testing of Shipping Containers
and
Systems", which is hereby incorporated, in its entirety, by reference thereto.
Of particular
interest is "12. Schedule D - Stacked Vibration and Schedule E - Vehicle
Vibration",
and still more particularly, Assurance Level II therein. This test method
evaluates the
ability of the package to undergo various vibrational frequencies for an
extended period,
which can cause flex cracking of a film surrounding a flowable product if the
film does
not exhibit satisfactory vibration abuse resistance. This test simulates
transport of the
package, particularly vehicular transport.
Another test for abuse resistance is known as the drop test. In testing the
retortable and retorted packaged product of the present invention, the drop
test is
preferably carried out by dropping 10 identical retorted packages onto a
concrete floor
from a height of 3 feet. The packages are inspected for seal breaks and film
rupture after
each drop, and the percentage of leaking packages is noted after each drop,
with the
leaking packages being discarded. The number of packages left (i.e., between 0
and 10)
multiplied by 10, is the percentage of packages which survive the drop test.
The multilayer retortable packaging films of the present invention are
preferably
irradiated to induce crosslinking of all of the layers. Crosslinking the
polymer in the
layers improves the ability of the film to withstand retorting. Preferably the
entire
multilayer structure of the film is crosslinked, and preferably the
crosslinking is induced
by irradiation of the film. In the irradiation process, the film is subjected
to an energetic
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radiation treatment, such as corona discharge, plasma, flame, ultraviolet, X-
ray, gamma
ray, beta ray, and high energy electron treatment, which induce cross-linking
between
molecules of the irradiated material. The irradiation of polymeric films is
disclosed in
U.S. Patent NO. 4,064,296, to BORNSTEIN, et. al., which is hereby incorporated
in its
entirety, by reference thereto. BORNSTEIN, et. al. discloses the use of
ionizing radiation
for crosslinking the polymer present in the film.
Radiation dosages are referred to herein in terms of the radiation unit "RAD",
with
one million RADS, also known as a megarad, being designated as "MR", or, in
terms of
the radiation unit kiloGray (kGy), with 10 kiloGray representing 1 MR, as is
known to
those of skill in the art. A suitable radiation dosage of high energy
electrons is in the
range of up to about 16 to 166 kGy, more preferably about 40 to 90 kGy, and
still more
preferably, 55 to 75 kGy. Preferably, irradiation is carried out by an
electron accelerator
and the dosage level is determined by standard dosimetry processes. Other
accelerators
such as a van der Graaf or resonating transformer may be used. The radiation
is not
limited to electrons from an accelerator since any ionizing radiation may be
used.
As used herein, the term "bag" is inclusive of L-seal bags, side-seal bags,
backseamed bags, and pouches. An L-seal bag has an open top, a bottom seal,
one side-
seal along a first side edge, and a seamless (i.e., folded, unsealed) second
side edge. A
side-seal bag has an open top, a seamless bottom edge, with each of its two
side edges
having a seal therealong. Although seals along the side and/or bottom edges
can be at the
very edge itself, (i.e., seals of a type commonly referred to as "trim
seals"), preferably the
seals are spaced inward (preferably 1/4 to 1/2 inch, more or less) from the
bag side edges,
and preferably are made using a impulse-type heat sealing apparatus, which
utilizes a bar
which is quickly heated and then quickly cooled. A backseamed bag is a bag
having an
open top, a seal running the length of the bag in which the bag film is either
fin-sealed or
lap-sealed, two seamless side edges, and a bottom seal along a bottom edge of
the bag. A
pouch is made from two films sealed together along the bottom and along each
side edge,
resulting in a U-seal pattern. Several of these various bag types are
disclosed in U.S.
Patent No. 6,790,468, to Mize et al, entitled "Patch Bag and Process of Making
Same",
the entirety of which is hereby incorporated by reference. In the Mize et al
patent, the
bag portion of the patch bag does not include the patch.
The term "polymer", as used herein, is inclusive of homopolymer, copolymer,
terpolymer, etc. "Copolymer" includes copolymer, terpolyrner, etc.
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As used herein, the phrase "heterogeneous polymer" refers to polymerization
reaction products of relatively wide variation in molecular weight and
relatively wide
variation in composition distribution, i.e., typical polymers prepared, for
example, using
conventional Ziegler-Natta catalysts. Heterogeneous copolymers typically
contain a
relatively wide variety of chain lengths and comonomer percentages.
Heterogeneous
copolymers have a molecular weight distribution (Mw/Mn) of greater than 3Ø
As used herein, the phrase "homogeneous polymer" refers to polymerization
reaction products of relatively narrow molecular weight distribution and
relatively narrow
composition distribution. Homogeneous polymers are useful in various layers of
the
multilayer film used in the present invention. Homogeneous polymers are
structurally
different from heterogeneous polymers, in that homogeneous polymers exhibit a
relatively even sequencing of comonomers within a chain, a mirroring of
sequence
distribution in all chains, and a similarity of length of all chains, i.e., a
narrower
molecular weight distribution. Furthermore, homogeneous polymers are typically
prepared using metallocene, or other single-site type catalysis, rather than
using Ziegler
Natta catalysts.
More particularly, homogeneous ethylene/alpha-olefin copolymers may be
characterized by one or more processes known to those of skill in the art,
such as
molecular weight distribution (Mw/Mn), Mz/Mn, composition distribution breadth
index
(CDBI), and narrow melting point range and single melt point behavior. The
molecular
weight distribution (Mw/Mn), also known as polydispersity, may be determined
by gel
permeation chromatography. The homogeneous ethylene/alpha-olefin copolymers
useful
in this invention generally has (Mw/Mn) of up to 3, more preferably up to 2.7;
more
preferably from about 1.9 to about 2.5; more preferably, from about 1.9 to
about 2.3. The
composition distribution breadth index (CDBI) of such homogeneous
ethylene/alpha-
olefin copolymers will generally be greater than about 70 percent. The CDBI is
defined
as the weight percent of the copolymer molecules having a comonomer content
within 50
percent (i.e., plus or minus 50%) of the median total molar comonomer content.
The
CDBI of linear polyethylene, which does not contain a comonomer, is defined to
be
100%. The Composition Distribution Breadth Index (CDBI) is determined via the
technique of Temperature Rising Elution Fractionation (TREF). CDBI
determination
clearly distinguishes the homogeneous copolymers (narrow composition
distribution as
assessed by CDBI values generally above 70%) from VLDPEs available
conunercially
which generally have a broad composition distribution as assessed by CDBI
values
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13
generally less than 55%. The CDBI of a copolyiner is readily calculated from
data
obtained from techniques known in the art, such as, for example, temperature
rising
elution fractionation as described, for example, in Wild et. al., J. Poly.
Sci. Poly. Phys.
Ed., Vol. 20, p.441 (1982). Preferably, homogeneous ethylene/alpha-olefin
copolymers
have a CDBI greater than about 70%, i.e., a CDBI of from about 70% to 99%. In
general,
the homogeneous ethylene/alpha-olefin copolymers in the patch bag of the
present
invention also exhibit a relatively narrow melting point range, in comparison
with
"heterogeneous copolymers", i.e., polymers having a CDBI of less than 55%.
Preferably,
the homogeneous ethylene/alpha-olefin copolymers exhibit an essentially
singular
melting point characteristic, with a peak melting point (Tm), as determined by
Differential Scanning Calorimetry (DSC), of from about 30 C to 130 C.
Preferably the
homogeneous copolymer has a DSC peak Tm of from about 80 C to 125 C. As used
herein, the phrase "essentially single melting point" means that at least
about 80%, by
weight, of the material corresponds to a single Tm peak at a temperature
within the range
of from about 60 C to 110 C, and essentially no substantial fraction of the
material has a
peak melting point in excess of about 130 C., as determined by DSC analysis.
DSC
measurements are made on a Perkin Elmer System 7 Thermal Analysis System.
Melting
information reported are second melting data, i.e., the sample is heated at a
programmed
rate of 10 C./min. to a temperature below its critical range. The sample is
then reheated
(2nd melting) at a programmed rate of 10 C/min. The presence of higher melting
peaks
is detrimental to film properties such as haze, and compromises the chances
for
meaningful reduction in the seal initiation temperature of the final film.
A homogeneous ethylene/alpha-olefin copolymer can, in general, be prepared by
the copolymerization of ethylene and any one or more alpha-olefin. Preferably,
the
alpha-olefin is a C3-C2o alpha-monoolefin, more preferably, a C4-C12 alpha-
monoolefin,
still more preferably, a C4-C8 alpha-monoolefin. Still more preferably, the
alpha-olefin
comprises at least one member selected from the group consisting of butene- 1,
hexene- 1,
and octene- 1, i.e., 1 -butene, 1 -hexene, and 1 -octene, respectively. Most
preferably, the
alpha-olefin comprises octene-1, and/or a blend of hexene-1 and butene-1.
Processes for preparing and using homogeneous polymers are disclosed in U.S.
Patent No. 5,206,075, U.S. Patent No. 5,241,031, and PCT International
Application WO
93/03093, each of which is hereby incorporated by reference thereto, in its
entirety.
Further details regarding the production and use of homogeneous ethylene/alpha-
olefin
copolymers are disclosed in PCT International Publication Number WO 90/03414,
and
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14
PCT International Publication Number WO 93/03093, both of which designate
Exxon
Chemical Patents, Inc. as the Applicant, and both of which are hereby
incorporated by
reference thereto, in their respective entireties.
Still another genus of homogeneous ethylene/alpha-olefin copolymers is
disclosed in U.S. Patent No. 5,272,236, to LAI, et. al., and U.S. Patent No.
5,278,272, to
LAI, et. al., both of which are hereby incorporated by reference thereto, in
their respective
entireties. Each of these patents disclose substantially linear homogeneous
long chain
branched ethylene/alpha-olefin copolymers produced and marketed by The Dow
Chemical Company.
As used herein, the phrase "ethylene/alpha-olefin copolymer", and
"ethylene/alpha-olefin copolymer", refer to such materials as linear low
density
polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE
and
ULDPE); and homogeneous polymers such as metallocene catalyzed polymers such
as
EXACT resins obtainable from the Exxon Chemical Company, and TAFMER resins
obtainable from the Mitsui Petrochemical Corporation; and single site
catalyzed Nova
SURPASS LLDPE (e.g., Surpass FPS 317-A, and Surpass FPS 117-C), and Sclair
VLDPE (e.g., Sclair FP112-A). All these materials generally include
copolymers of
ethylene with one or more comonomers selected from C4 to Clo alpha-olefin such
as
butene-1 (i.e., 1-butene), hexene- 1, octene- 1, etc. in which the molecules
of the
copolymers comprise long chains with relatively few side chain branches or
cross-linked
structures. This molecular structure is to be contrasted with conventional low
or medium
density polyethylenes which are more highly branched than their respective
counterparts.
The heterogeneous ethylene/alpha-olefins commonly known as LLDPE have a
density
usually in the range of from about 0.91 grams per cubic centimeter to about
0.94 grams
per cubic centimeter. Other ethylene/alpha-olefin copolymers, such as the long
chain
branched homogeneous ethylene/alpha-olefin copolymers available from the Dow
Chemical Company, known as AFFINITY resins, are also included as another type
of
homogeneous ethylene/alpha-olefin copolymer useful in the present invention.
As used herein, the expression "C2_3/C3_20 copolymer" is inclusive of a
copolymer
of ethylene and a C3 to C20 alpha-olefin and a copolymer of propylene and a C4
to C20
alpha-olefin. Similar expressions are to be interpreted in a corresponding
manner.
As used herein, the phrase "very low density polyethylene" refers to
heterogeneous ethylene/alpha-olefin copolymers having a density of 0.915 g/cc
and
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below, preferably from about 0.88 to 0.915 g/cc. As used herein, the phrase
"linear low
density polyethylene" refers to, and is inclusive of, both heterogeneous and
homogeneous
ethylene/alpha-olefin copolymers having a density of at least 0.915 g/cc,
preferably from
0.916 to 0.94 g/cc.
5 As used herein, the term "bag" is inclusive of L-seal bags, side-seal bags,
backseamed bags, and pouches. An L-seal bag has an open top, a bottom seal,
one side-
seal along a first side edge, and a seamless (i.e., folded, unsealed) second
side edge. A
side-seal bag has an open top, a seamless bottom edge, with each of its two
side edges
having a seal therealong. Although seals along the side and/or bottom edges
can be at the
10 very edge itself, (i.e., seals of a type commonly referred to as "trim
seals"), preferably the
seals are spaced inward (preferably 1/4 to 1/2 inch, more or less) from the
bag side edges,
and preferably are made using a impulse-type heat sealing apparatus, which
utilizes a bar
which is quickly heated and then quickly cooled. A backseamed bag is a bag
having an
open top, a seal running the length of the bag in which the bag film is either
fin-sealed or
15 lap-sealed, two seamless side edges, and a bottom seal along a bottom edge
of the bag. A
pouch is made from two films sealed together along the bottom and along each
side edge,
resulting in a U-seal pattern. Several of these various bag types are
disclosed in U.S.
Patent No. 6,790,468, to Mize et al, entitled "Patch Bag and Process of Making
Same",
the entirety of which is hereby incorporated by reference. In the Mize et al
patent, the
bag portion of the patch bag does not include the patch. Packages produced
using a form-
fill-seal process are set forth in USPN 4,589,247, discussed above.
Casings are also included in the group of packaging articles in accordance
with
the present invention. Casings include seamless tubing casings which have
clipped or
sealed ends, as well as backseamed casings. Backseamed casings include lap-
sealed
backseamed casings (i.e., backseam seal of the inside layer of the casing to
the outside
layer of the casing, i.e., a seal of one outer film layer to the other outer
film layer of the
same film), fin-sealed backseained casings (i.e., a backseam seal of the
inside layer of the
casing to itself, with the resulting "fin" protruding from the casing), and
butt-sealed
backseamed casings in which the longitudinal edges of the casing film are
abutted against
one another, with the outside layer of the casing film being sealed to a
backseaming tape.
Each of these embodiments is disclosed in USPN 6,764,729 B2, to Ramesh et al,
entitled
"Backseamed Casing and Packaged Product Incorporating Same, which is hereby
incorporated in its entirety, by reference thereto.
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16
Examples 1-6
The following multilayer retortable films were prepared using the flat cast
film
production process illustrated in FIG. 1. Resin pellets 10 were fed into
hopper 12 and
melted, forwarded, and degassed in extruder 14. For convenience, only one
hopper and
extruder are illustrated in FIG. 1. However, there was a hopper, and extruder
for each of
the nine layers of the multilayer film being prepared. The molten streams from
each of
extruders 14 were fed into multilayer slot die 16, from which the streams
emerged as
multilayer extrudate 18. Multilayer extrudate 18 was cast downwardly from die
16 onto
rotating casting drum 20, which had a diameter of about 43 inches and was
maintained at
40 F.
Shortly after contacting casting drum 20, extrudate 18 solidified and was
cooled
by water from water knife 22, forming multilayer film 19. Multilayer film 19
passed in
partial wrap around casting drum 20, being dried by air from air from air
knife 21, and
was thereafter passed in partial wrap around a first chill roll 24 and then in
partial wrap
around second chill ro1126. Chill rolls 24 and 26 had a diameter of about 18
inches and
were maintained at room temperature. Multilayer film 19 then passed over
feeder roller
28, and is illustrated as then being passed through irradiation chamber 30 and
receiving
40 kGy of electron beam irradiation, resulting in retortable crosslinked
multilayer film 32
and is wound up on winder 34. In reality, however, multilayer film 19 was
first wound
up, then unwound and fed through irradiation chamber 30 where it was subjected
to 40
kGy of electron beam irradiation, resulting in retortable crosslinked
multilayer film 32.
The layer composition, layer order, layer function, and layer thickness of
each of
the 9 layers for the films of Examples 1 through 6 are set forth in Table 1,
below. The
Table of Materials (below Table 1) provides density, melt index, and generic
chemical
composition description of the various tradename resins set forth in Table 1.
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17
Table 1(Films of Examples 1, 2, 3, and 4)
Film of Layer Layer Layer Layer Layer Layer Layer Layer Layer
Example No.1 No.2 No.3 No.4 No.5 No. 6 No.7 No.8 No. 9
Number
(skin) (tie) (high (oxygen (high (grease (grease (seal and
temp barrier) temp resist and resist food
abuse) abuse) tie) and tie) contact)
Atofina Mitsui Mitsui BASF EMS BASF Equistar Equistar Atofina
EODO1-03 Admer Admer Ultramid Grivory Ultramid Plexar Plexar EODOl-03
(48%) 1053A 1167A B40 G21 B40 2246 2246 (48%)
(70%) (70%) (60%) (60%)
ExxonMobil ExxonMobil
Exact3128 Aegis Aegis Plexar Plexar Exact3128
(44%) (tie and HCA73QP HCA73QP 2220 2220 (44%)
low (30%) (30%) (40%) (40%)
SLIP/AB temp SLIP/AB
8%) abuse) (blend of (blend of 8%)
high & high &
med temp med temp
abuse) abuse)
Mils 1.0 0.50 1.0 0.60 0.30 0.60 0.24 0.36 1.40
Atofina Mitsui BASF BASF EMS BASF Equistar Equistar Atofina
EODO1-03 Admer Ultramid Ultramid Grivory Ultramid Plexar Plexar EODOl-03
(48%) 1053A C40 B40 G21 B40 2246 2246 (48%)
(60%) (60%)
ExxonMobil (medium ExxonMobil
2 Exact3128 temp Plexar Plexar Exact3128
(44%) abuse) 2220 2220 (44%)
(40%) (40%)
SLIP/AB SLIP/AB
8%) 8%)
Mils 1.0 1.1 0.40 0.60 0.30 0.60 0.24 0.36 1.40
Atofina Mitsui BASF BASF EMS BASF DuPont Equistar Atofina
EODOI-03 Admer Ultramid Ultramid Grivory Ultramid Surlyn Plexar EODOI-03
(48%) 1053A C40 B40 G21 B40 1650 2246 (48%)
3 (60%)
ExxonMobil Medium Fat ExxonMobil
Exact3128 temp Resistance Plexar Exact3128
(44%) Abuse & 2220 (44%)
Tie (40%)
SLIP/AB SLIP/AB
8%) 8%)
Mils 1.0 1.1 0.40 0.60 0.30 0.60 0.24 0.36 1.40
Atofina Mitsui BASF BASF EMS BASF DuPont Equistar Atofina
EODOI-03 Admer Ultramid Ultramid Grivory Ultramid Surlyn Plexar EODO1-03
(480%) 1053A C40 B40 G21 B40 1857 2246 (48%)
4
ExxonMobil Medium Fat (60%) ExxonMobil
Exact3128 temp Resistance Plexar Exact3128
(44%) Abuse & 2220 (44%)
Tie (40%)
SLIP/AB SLIP/AB
8%) 8%)
Mils 1.0 1.1 0.40 0.60 0.30 0.60 0.24 0.36 1.40
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18
Atofina Mitsui BASF BASF EMS BASF DuPont Equistar Atofina
EOD01-04 Admer Ultramid Ultramid Grivory Ultramid Surlyn Plexar EODO1-04
(48%) 1053A C40 B40 G21 B40 1857 2246 (48%)
ExxonMobil Medium Fat (60%) ExxonMobil
Exact3128 temp Resistance Plexar Exact3128
(44%) Abuse & 2220 (44%)
Tie (40%)
SLIP/AB SLIP/AB
8%) 8%)
Mils 1.0 1.1 0.40 0.60 0.30 0.60 0.24 0.36 1.40
Atofina Mitsui BASF BASF EMS BASF DuPont Equistar Atofina
EOD01-03 Admer Ultramid Ultramid Grivory Ultramid Surlyn Plexar EOD03-01
(48%) 1053A C40 B40 G21 B40 1857 2246 (48%)
6 ExxonMobil Medium Fat (60%) ExxonMobil
Exact3128 temp Resistance Plexar Exact3128
(44%) Abuse & 2220 (44%)
Tie (40%)
SLIP/AB SLIP/AB
8%) 8%)
Mils 1.0 1.1 0.40 0.60 0.30 0.60 0.24 0.36 1.40
Table of Materials
5
Material Densi MI Composition
Slip/AB 0.95 1.8 dg/min Slip and
=Slip and measured using antiblocking agents
Antiblocking ASTM D1238, @ in a Ziegler Natta
Masterbatch 190 C and 2.16 Kg catalyzed linear low
=Ampacet 102729 density
polyethylene carrier
Atofina 0.90 8.0(dg/min) Metallocene
EOD01-03 measured using catalyzed isotactic
ASTM D 1238 @ polypropylene
230 C and 2.16 Kg
Atofina 0.90 8.0 dg/min Metallocene
EODO1-04 measured using catalyzed isotactic
ASTM D 1238 @ polypropylene
230 C and 2.16 Kg
Atofina 0.90 5.0 dg/min Metallocene
EOD03-01 measured using catalyzed isotactic
ASTM D 1238 @ polypropylene
230 C and 2.16 Kg
Exxon Exact 3128 0.90 1.0 dg/min Metallocene
measured using catalyzed ethylene/
ASTM D1238, @ butene copolymer
190 C and 2.16 Kg
Admer 0.91 1.0 dg/min Anhydride grafted
AT1053A measured using LLDPE tie
ASTM D1238, @
190 C and 2.16 Kg
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19
Admer 0.91 2.0 dg/min Anhydride grafted
AT1167A measured using LLDPE tie
ASTM D1238, @
190 C and 2.16 Kg
Equistar Plexar 0.951 0.6 dg/min Anhydride grafted
2246 measured using HDPE tie
ASTM D1238, @
190 C and 2.16 Kg
Equistar Plexar 0.943 5.5 dg/min Anhydride grafted
2220 measured using HDPE tie
ASTM D1238, @
190 C and 2.16 Kg
BASF C40 1.13 --- PA-6/6,6
BASF B40 1.14 --- PA-6
EMS G21 1.18 --- Amorphous
PA-61/6T
AEGIS HCA73QP 1.13 --- Semicrystalline
PA-6/6,6
Surlyn 1650 0.94 1.5 dg/min Zinc ionomer resin
measured using
ASTM D1238, @
190 C and 2.16 Kg
Surlyn 1857 0.94 4.0 dg/min Zinc ionomer resin
measured using
ASTM D1238, @
190 C and 2.16 Kg
Although the present invention has been described with reference to the
preferred
embodiments, it is to be understood that modifications and variations of the
invention
exist without departing from the principles and scope of the invention, as
those skilled in
the art will readily understand. Accordingly, such modifications are in
accordance with
the claims set forth below
